It lies between the Vipava Valley, the low hills surrounding the valley, the westernmost part of the Brkini Hills, northern Istria, and the Gulf of Trieste. The western edge of the plateau also marks the traditional ethnic border between Italians and Slovenes. The region gave its name to the karst topography. For this reason, it is also referred to as the Classical Karst.
The plateau rises quite steeply above the neighboring landscape, except for its northeastern side, where the steepness is less pronounced. The plateau gradually descends from the southeast to the southwest. On average it lies 334 m above sea level. Its western edge, known as the Karst Rim (Slovene: Kraški rob), is a continuation of the Učka mountain range in eastern Istria, and rises to the east and southeast of Trieste, ending in steep cliffs between Aurisina and Duino. Many interesting geological phenomena occur along the Karst Rim, including the picturesque Rosandra Valley (also known as Glinščica).
Because the Karst steeply descends towards the Adriatic Sea, it is less exposed to the beneficial climatological effects of the Mediterranean. In the past, the main vegetation on the plateau was oaks, but these were replaced by pine forests in the 19th and 20th centuries. Forests now cover only one-third of the Karst. Starting the Middle Ages, the plateau suffered radical deforestation for economic reasons. Although much of the wood for the closely spaced piles that support the island city of Venice, Italy came from this region, Venice carefully managed the Karst forests as a reserve for naval timber. The most radical deforestation occurred in the mid-nineteenth century due to clear-cutting by local farmers and conversion of the land into pastures for sheep.
The Karst is famous for its caves. In Slovenia, they include Vilenica Cave (the oldest show cave in Europe), Lipica Cave, Divača Cave, Kačna Cave, Postojna Cave, and Škocjan Caves (a UNESCO World Heritage Site), and Grotta Gigante in Italy (the largest show cave in the world).
Most of the Karst is located in the Slovenian Littoral, covering an area of 429 square kilometres, with a population of about 19,000 people. The Karst as a whole has exactly 100 settlements. The town of Sežana is the center of the region on the Slovene side of the border. The main rural centers are the settlements of Divača, Dutovlje, and Komen. Štanjel is a picturesque clustered settlement at the top of the northern rim of the plateau; its houses are tightly clustered around Turn Hill, giving it the appearance of a medieval town. On the Italian side of the border, important settlements include Opicina, Duino, and Aurisina.
Natural conditions, including the bora (Slovene: burja) wind, and the local way of life all shaped the elements of Karst architecture, creating simple but well-defined forms. One of the main tourist centers in the area is Lipica, with its stud farm (the home of the Lipizzan horse breed) as well as other tourist facilities.
The vast majority of the inhabitants of the Karst Plateau are ethnic Slovenes. Traditionally, only the village of San Martino del Carso (in the municipality of Sagrado), has been inhabited by Friulian speakers, while all the rest of the region was almost entirely Slovene-speaking from the Middle Ages till the late 1940s and 1950s, when Istrian Italians fleeing from Yugoslavia were settled in Karstic villages in the Province of Trieste, especially in the municipality of Duino. As a consequence, today an estimated one fifth of the population of the Karst Plateau is Italian speaking, while the rest is mostly Slovene speaking.